1. Field of the Invention
The present invention relates to an automobile speed control system for setting, memorizing and cancelling desired target speeds in an apparatus for enabling an automobile to travel at a desired constant target speed.
2. Description of the Prior Art
Automobile speed control systems of the type described above detect an actual automobile speed as a number of pulses and produce as a speed signal an analog voltage proportional to the number of pulses generated. When the automobile as it runs has reached a desired speed, the driver turns on a constant-speed travel setting switch to enable a memory circuit to set or store the speed signal at that time. The speed control system includes a comparator to which there are applied a reference voltage indicative of the set speed signal and a voltage representative of the current speed of the automobile. The speed control system adjusts the opening of the throttle valve in order to eliminate any difference between the reference voltage and the actual-speed voltage.
The automobile speed control systems have a deceleration setting function for allowing the automobible speed to slow down gradually as long as the driver pushes or closes the constant-speed travel setting switch after the automobile has run at a constant speed, and for bringing the automobile into a constant-speed travel mode by enabling the memory circuit to store the automobile speed available at the instant the setting switch is opened. Some speed control systems also include a "tap-up" function for causing the automobile speed to increase slightly when the driver momentarily actuates the setting switch while the automobile is running at a constant speed. Therefore, the automobile can be decelerated as long as the setting switch is depressed and be accelerated when the setting switch is operated upon momentarily.
With the tap-up function, however, the automobile speed increases only a small fraction ranging from 1 to 5 km/h each time the setting switch is flipped. When it is desired to increase the car speed to a great extent, the driver is required to actuate the setting switch repeatedly. Thus, the operation for a speed increase is awkward and it takes a long period of time for the automobile to reach a desired speed through the operation of the setting switch.
The apparatus for controlling the automobile to run at a desired constant speed is normally arranged such that the constant-speed travel mode is automatically released or disabled for safety purpose when a brake pedal is depressed while the automobile is running in that constant-speed travel mode. The apparatus is equipped with a resume switch for enabling the automobile to regain the previously memorized speed after the brake pedal has been released.